6 The AltOS firmware build for the altimeters has two
7 fundamental modes, “idle” and “flight”. Which of these modes
8 the firmware operates in is determined at start up time. For
9 TeleMetrum, TeleMega and EasyMega, which have accelerometers, the mode is
10 controlled by the orientation of the
11 rocket (well, actually the board, of course...) at the time
12 power is switched on. If the rocket is “nose up”, then
13 the flight computer assumes it's on a rail or rod being prepared for
14 launch, so the firmware chooses flight mode. However, if the
15 rocket is more or less horizontal, the firmware instead enters
16 idle mode. Since TeleMini v2.0 and EasyMini don't have an
17 accelerometer we can use to determine orientation, “idle” mode
18 is selected if the board is connected via USB to a computer,
19 otherwise the board enters “flight” mode. TeleMini v1.0
20 selects “idle” mode if it receives a command packet within the
21 first five seconds of operation.
23 At power on, the altimeter will beep out the battery voltage
24 to the nearest tenth of a volt. Each digit is represented by
25 a sequence of short “dit” beeps, with a pause between
26 digits. A zero digit is represented with one long “dah”
27 beep. Then there will be a short pause while the altimeter
28 completes initialization and self test, and decides which mode
31 In flight or “pad” mode, the altimeter engages the flight
32 state machine, goes into transmit-only mode to send telemetry,
33 and waits for launch to be detected. Flight mode is indicated
34 by an “di-dah-dah-dit” (“P” for pad) on the beeper or lights,
35 followed by beeps or flashes indicating the state of the
36 pyrotechnic igniter continuity. One beep/flash indicates
37 apogee continuity, two beeps/flashes indicate main continuity,
38 three beeps/flashes indicate both apogee and main continuity,
39 and one longer “brap” sound which is made by rapidly
40 alternating between two tones indicates no continuity. For a
41 dual deploy flight, make sure you're getting three beeps or
42 flashes before launching! For apogee-only or motor eject
43 flights, do what makes sense.
45 If idle mode is entered, you will hear an audible “di-dit” or
46 see two short flashes (“I” for idle), and the flight state
47 machine is disengaged, thus no ejection charges will fire.
48 The altimeters also listen for the radio link when in idle
49 mode for requests sent via TeleDongle. Commands can be issued
50 in idle mode over either USB or the radio link
51 equivalently. TeleMini v1.0 only has the radio link. Idle
52 mode is useful for configuring the altimeter, for extracting
53 data from the on-board storage chip after flight, and for
54 ground testing pyro charges.
56 In “Idle” and “Pad” modes, once the mode indication
57 beeps/flashes and continuity indication has been sent, if
58 there is no space available to log the flight in on-board
59 memory, the flight computer will emit a warbling tone (much
60 slower than the “no continuity tone”)
62 See <<_understanding_beeps>> for a summary of all of
63 the audio signals used.
65 Once landed, the flight computer will signal that by emitting
66 the “Landed” sound described above, after which it will beep
67 out the apogee height (in meters). Each digit is represented
68 by a sequence of short “dit” beeps, with a pause between
69 digits. A zero digit is represented with one long “dah”
70 beep. The flight computer will continue to report landed mode
71 and beep out the maximum height until turned off.
73 One “neat trick” of particular value when TeleMetrum, TeleMega
74 or EasyMega are used with
75 very large air-frames, is that you can power the board up while the
76 rocket is horizontal, such that it comes up in idle mode. Then you can
77 raise the air-frame to launch position, and issue a 'reset' command
78 via TeleDongle over the radio link to cause the altimeter to reboot and
79 come up in flight mode. This is much safer than standing on the top
80 step of a rickety step-ladder or hanging off the side of a launch
81 tower with a screw-driver trying to turn on your avionics before
84 TeleMini v1.0 is configured solely via the radio link. Of course, that
85 means you need to know the TeleMini radio configuration values
86 or you won't be able to communicate with it. For situations
87 when you don't have the radio configuration values, TeleMini v1.0
88 offers an 'emergency recovery' mode. In this mode, TeleMini is
89 configured as follows:
92 * Sets the radio frequency to 434.550MHz
93 * Sets the radio calibration back to the factory value.
94 * Sets the callsign to N0CALL
95 * Does not go to 'pad' mode after five seconds.
97 To get into 'emergency recovery' mode, first find the row of
98 four small holes opposite the switch wiring. Using a short
99 piece of small gauge wire, connect the outer two holes
100 together, then power TeleMini up. Once the red LED is lit,
101 disconnect the wire and the board should signal that it's in
102 'idle' mode after the initial five second startup period.
106 TeleMetrum and TeleMega include a complete GPS receiver. A
107 complete explanation of how GPS works is beyond the scope of
108 this manual, but the bottom line is that the GPS receiver
109 needs to lock onto at least four satellites to obtain a solid
110 3 dimensional position fix and know what time it is.
112 The flight computers provide backup power to the GPS chip any time a
113 battery is connected. This allows the receiver to “warm start” on
114 the launch rail much faster than if every power-on were a GPS
115 “cold start”. In typical operations, powering up
116 on the flight line in idle mode while performing final air-frame
117 preparation will be sufficient to allow the GPS receiver to cold
118 start and acquire lock. Then the board can be powered down during
119 RSO review and installation on a launch rod or rail. When the board
120 is turned back on, the GPS system should lock very quickly, typically
121 long before igniter installation and return to the flight line are
124 === Controlling An Altimeter Over The Radio Link
126 One of the unique features of the Altus Metrum system is the
127 ability to create a two way command link between TeleDongle
128 and an altimeter using the digital radio transceivers
129 built into each device. This allows you to interact with the
130 altimeter from afar, as if it were directly connected to the
133 Any operation which can be performed with a flight computer can
134 either be done with the device directly connected to the
135 computer via the USB cable, or through the radio
136 link. TeleMini v1.0 doesn't provide a USB connector and so it is
137 always communicated with over radio. Select the appropriate
138 TeleDongle device when the list of devices is presented and
139 AltosUI will interact with an altimeter over the radio link.
141 One oddity in the current interface is how AltosUI selects the
142 frequency for radio communications. Instead of providing
143 an interface to specifically configure the frequency, it uses
144 whatever frequency was most recently selected for the target
145 TeleDongle device in Monitor Flight mode. If you haven't ever
146 used that mode with the TeleDongle in question, select the
147 Monitor Flight button from the top level UI, and pick the
148 appropriate TeleDongle device. Once the flight monitoring
149 window is open, select the desired frequency and then close it
150 down again. All radio communications will now use that frequency.
152 * Save Flight Data—Recover flight data from the
153 rocket without opening it up.
155 * Configure altimeter apogee delays, main deploy
156 heights and additional pyro event conditions to
157 respond to changing launch conditions. You can also
158 'reboot' the altimeter. Use this to remotely enable
159 the flight computer by turning TeleMetrum or
160 TeleMega on in “idle” mode, then once the air-frame
161 is oriented for launch, you can reboot the
162 altimeter and have it restart in pad mode without
163 having to climb the scary ladder.
165 * Fire Igniters—Test your deployment charges without snaking
166 wires out through holes in the air-frame. Simply assemble the
167 rocket as if for flight with the apogee and main charges
168 loaded, then remotely command the altimeter to fire the
171 Operation over the radio link for configuring an
172 altimeter, ground testing igniters, and so forth uses
173 the same RF frequencies as flight telemetry. To
174 configure the desired TeleDongle frequency, select the
175 monitor flight tab, then use the frequency selector
176 and close the window before performing other desired
179 The flight computers only enable radio commanding in
180 'idle' mode. TeleMetrum and TeleMega use the
181 accelerometer to detect which orientation they start
182 up in, so make sure you have the flight computer lying
183 horizontally when you turn it on. Otherwise, it will
184 start in 'pad' mode ready for flight, and will not be
185 listening for command packets from TeleDongle.
187 TeleMini listens for a command packet for five seconds
188 after first being turned on, if it doesn't hear
189 anything, it enters 'pad' mode, ready for flight and
190 will no longer listen for command packets. The easiest
191 way to connect to TeleMini is to initiate the command
192 and select the TeleDongle device. At this point, the
193 TeleDongle will be attempting to communicate with the
194 TeleMini. Now turn TeleMini on, and it should
195 immediately start communicating with the TeleDongle
196 and the desired operation can be performed.
198 You can monitor the operation of the radio link by watching the
199 lights on the devices. The red LED will flash each time a packet
200 is transmitted, while the green LED will light up on TeleDongle when
201 it is waiting to receive a packet from the altimeter.
205 An important aspect of preparing a rocket using electronic deployment
206 for flight is ground testing the recovery system. Thanks
207 to the bi-directional radio link central to the Altus Metrum system,
208 this can be accomplished in a TeleMega, TeleMetrum or TeleMini equipped rocket
209 with less work than you may be accustomed to with other systems. It
212 Just prep the rocket for flight, then power up the altimeter
213 in “idle” mode (placing air-frame horizontal for TeleMetrum or TeleMega, or
214 selecting the Configure Altimeter tab for TeleMini). This will cause
215 the firmware to go into “idle” mode, in which the normal flight
216 state machine is disabled and charges will not fire without
217 manual command. You can now command the altimeter to fire the apogee
218 or main charges from a safe distance using your computer and
219 TeleDongle and the Fire Igniter tab to complete ejection testing.
223 TeleMetrum, TeleMini and TeleMega all incorporate an
224 RF transceiver, but it's not a full duplex system;
225 each end can only be transmitting or receiving at any
226 given moment. So we had to decide how to manage the
229 By design, the altimeter firmware listens for the
230 radio link when it's in “idle mode”, which allows us
231 to use the radio link to configure the rocket, do
232 things like ejection tests, and extract data after a
233 flight without having to crack open the air-frame.
234 However, when the board is in “flight mode”, the
235 altimeter only transmits and doesn't listen at all.
236 That's because we want to put ultimate priority on
237 event detection and getting telemetry out of the
238 rocket through the radio in case the rocket crashes
239 and we aren't able to extract data later.
241 We don't generally use a 'normal packet radio' mode
242 like APRS because they're just too inefficient. The
243 GFSK modulation we use is FSK with the base-band
244 pulses passed through a Gaussian filter before they go
245 into the modulator to limit the transmitted bandwidth.
246 When combined with forward error correction and
247 interleaving, this allows us to have a very robust
248 19.2 kilobit data link with only 10-40 milliwatts of
249 transmit power, a whip antenna in the rocket, and a
250 hand-held Yagi on the ground. We've had flights to
251 above 21k feet AGL with great reception, and
252 calculations suggest we should be good to well over
253 40k feet AGL with a 5-element yagi on the ground with
254 our 10mW units and over 100k feet AGL with the 40mW
255 devices. We hope to fly boards to higher altitudes
256 over time, and would of course appreciate customer
257 feedback on performance in higher altitude flights!
259 :aprsdevices: TeleMetrum v2.0 and TeleMega
260 :configure_section: _configure_altimeter
261 include::aprs-operation.raw[]
263 === Configurable Parameters
265 Configuring an Altus Metrum altimeter for flight is
266 very simple. Even on our baro-only TeleMini and
267 EasyMini boards, the use of a Kalman filter means
268 there is no need to set a “mach delay”. All of the
269 configurable parameters can be set using AltosUI
270 over USB or or radio link via TeleDongle. Read
271 <<_configure_altimeter>> for more information.
projects / fw / altos / blob